EXHIBIT 5.1

                               OPINION OF COUNSEL

June 30, 2003

Mercury Interactive Corporation
1325 Borregas Avenue
Sunnyvale, California 94089

     RE:  Registration Statement on Form S-8

Ladies and Gentlemen:

We have examined the Registration Statement on Form S-8 to be filed by you with
the Securities and Exchange Commission on or about June 30, 2003 (the
"Registration Statement") in connection with the registration under the
Securities Act of 1933, as amended, of a total of 9,303 shares of your Common
Stock (the "Shares") reserved for issuance under the Performant, Inc. 2000 Stock
Option/Restricted Stock Plan (the "Plan"). As legal counsel for Mercury
Interactive Corporation, we have examined the proceedings taken and are familiar
with the proceedings proposed to be taken by you in connection with the sale and
issuance of the Shares under the Plan.

It is our opinion that, when issued and sold in the manner referred to in the
Plan and pursuant to the agreement which accompanies each grant under the Plan,
the Shares will be legally and validly issued, fully paid and nonassessable.

We consent to the use of this opinion as an exhibit to the Registration
Statement and further consent to the use of our name wherever it appears in the
Registration Statement and any amendments thereto.

                                                        Very truly yours,

                                                        GCA LAW PARTNERS LLP

                                                        /s/ GCA Law Partners LLP